Voltage regulators are circuits that are used to provide a regulated voltage for use by other power consumption circuitry. For example, voltage regulators are included in many integrated circuits, for providing stable voltages at a variety of voltage levels. The requirements from the power consumption circuitry for voltage, current, or a combination thereof may vary depending on operation conditions and functional operations of the power consumption circuitry. This variable demand can cause the magnitude of the regulated voltage to vary as well. The voltage regulator, however, is supposed to adjust to the varying needs and changes so that the regulated output voltage maintains a relatively stable voltage level.
FIG. 1 illustrates a conventional voltage regulator 100 for providing a regulated output voltage 150 (Vout). The voltage regulator 100 includes a differential amplifier 110 providing a difference voltage 115 (Vdiff) based on the voltage difference between a reference voltage 105 (Vref) and a feedback voltage 145 (Vmon). The difference voltage 115 from the differential amplifier 110 is coupled to a gate of a p-channel transistor 120 that drives the regulated output voltage 150 in accordance with the output voltage of the differential amplifier 110. Resistance R1 130 and resistance R2 140 are coupled in series to the drain of the p-channel transistor 120. A combination of the resistance 130 and the resistance 140 may be used to set the voltage magnitude of the output voltage 150. In particular, for the voltage regulator 100, Vout=(1+R2/R1)×Vref. The resistances R1 and R2 are also configured as a voltage divider to provide an appropriate feedback voltage 145 to the differential amplifier 110 for comparison to the reference voltage 105.
In operation, the magnitude of the output voltage 150 is monitored through a feedback loop providing the feedback voltage 145 to the differential amplifier 110. In response, the differential amplifier 110 varies the conductivity of the p-channel transistor 120 that drives the output voltage 150 in accordance with the difference between the feedback voltage 145 and the reference voltage 105. For example, when the feedback voltage 145 is less than the reference voltage 105, the differential amplifier 110 provides a voltage to the gate of the p-channel transistor 120 to be more conductive, thereby driving the output voltage 150 to a higher level. Conversely, when the feedback voltage 145 is greater than the reference voltage 105, the differential amplifier 110 provides a voltage to the gate of the p-channel transistor 120 to be less conductive, thereby driving the output voltage 150 to a lower level.
However, this feedback mechanism can react relatively slowly to rapid changes in power demands from the power consumption circuitry coupled to the output voltage 150. There is a need for methods and apparatuses for providing a stable output voltage that reacts more quickly in response to rapid changes on power requirements.